The present invention relates generally to battery charging systems, and, more particularly, to a battery charging system, and associated method therefor, for initiating fast charging of a battery.
Powering of an electrical device requires the device to be supplied with electrical power of levels sufficient to effectuate the operation thereof. In many instances, the power required to operate the electrical device is supplied by one or more batteries electrically coupled to the electrical device. The use of a battery to power the electrical device is necessitated, in some instances, to permit operation of the electrical device when the electrical device is not, or cannot be, positioned proximate to a permanent power supply. In other instances, the electrical device is powered by the battery to increase the portability of the electrical device.
When the electrical device is powered by a battery, the period of time during which the electrical device may be operated is limited by the energy storage capacity of the battery. A battery stores only a finite amount of energy, and such energy stored by the battery is utilized to power the electrical device during operation thereof. As the battery is utilized to power the electrical device, the stored energy of the battery is depleted, and the battery becomes discharged. Once the battery becomes discharged, replacement of the battery is required to permit continued operation of the electrical device.
A portable or transportable radiotelephone is one such electrical device which is commonly powered by a battery. Operation of the radiotelephone to transmit or to receive a modulated, information signal requires power levels of up to three watts to be supplied to the radiotelephone. Commercially available batteries constructed to power such a portable or transportable radiotelephone at such a power level store amounts of energy to permit operation of the radiotelephone at such a power level for approximately one hour. If the battery is not initially fully charged, the operational period during which the radiotelephone may be operated, is, of course, commensurately reduced.
Once a battery has been discharged beneath a certain level, responsive to powering of the radiotelephone or otherwise, the battery coupled to power the radiotelephone must be removed and replaced with another battery to permit continued operation of the radiotelephone.
Commercially available, rechargeable batteries have been developed which may be recharged to be reused thereafter to power again an electrical device. Rechargeable battery constructions, are, for example, commercially available for use with portable and transportable radiotelephones. One such rechargeable battery may be recharged, and reused, up to, or even in excess of, five hundred times.
Typically, a rechargeable battery construction, although generically referred to as a battery, is actually comprised of a number of individual battery cells which are connected theretogether to generate desired, output voltages and currents. The battery cells are housed within a housing wherein the housing, together with the plurality of battery cells, is referred to as a "battery pack". For purposes of simplicity, such constructions are many times referred to simply by the term "battery". The instant disclosure utilizes such terminology except when, and as shall be noticed hereinbelow, the more precise terminology is required.
Battery charging apparatus is similarly commercially available to permit recharging of one or more such rechargeable batteries. A battery charger is typically comprised of a support structure for supporting one or more batteries, and apparatus for supplying a charging current for charging the batteries when suitably positioned upon the support structure. The rechargeable battery may be recharged responsive to application thereto of a charging current generated by the current source for a period of time. The time period required to charge fully the rechargeable battery is dependent upon the battery type, the extent to which the battery has been discharged, and the magnitude of the charging current applied to the batteries.
Certain battery charging constructions supply a relatively small magnitude current (such as, for example, a C/10 value wherein C is defined to be the one-hour capacity of a battery) to the batteries, and other battery charging constructions supply a significantly larger current (such as, for example, a C value) to the batteries. Application of the large magnitude current to the batteries is referred to as fast charging of the batteries. Application of the small magnitude current to the batteries is referred to as trickle charging of the batteries. Several battery charging constructions permit the application of either the large current (i.e., the fast charging current), or the relatively small current (i.e., the trickle charging current) to be applied to the battery to recharge the battery thereby.
When a large magnitude charging current is applied to the battery to recharge the battery thereby, the time required to recharge the rechargeable battery is less than the time required to recharge the same rechargeable battery when a small magnitude charging current is applied to the battery. Therefore, for reasons of convenience, charging of a rechargeable battery through application of a fast charging current thereto is advantageous. However, the rechargeable battery must be of a construction to permit application of a fast charging current thereto. A rechargeable battery comprised of a nickel-cadmium (Ni-Cd) material constitutes one type of rechargeable battery construction which may be recharged by the application of a fast charging current thereto.
Even when the rechargeable battery is constructed of a nickel-cadmium material, or some other such material which may be recharged by the application of a fast charging current thereto, care must be exercised to ensure that application of the fast charging current to the battery does not cause the battery to become damaged. For instance, when a fast charging current is applied to a rechargeable battery, a portion of the energy of the charging current is converted into heat energy. Such conversion results in an elevation of the battery temperature. If the ambient temperature of the battery is initially (prior to application of the charging current) above a maximum level, the heat energy generated during application of the fast charging current to the rechargeable battery can cause damage to the battery. Therefore, when the ambient temperature level of the battery is above a maximum value, the fast charging current should not be applied to the battery to recharge the battery. A trickle charging current may, however, normally be applied to the rechargeable battery even when the temperature level of the battery is too high to apply a fast charging current thereto because the magnitude of heat energy generated during application of a trickle charging current to the rechargeable battery does not result in a significant temperature increase of the battery.
Conversely, when the ambient temperature level of the battery is below a minimum value, application of the fast charging current to the rechargeable battery can also cause damage to the battery. Therefore, fast charging current should not be applied to the battery when the ambient temperature of the battery is beneath a minimum value.
Additionally, damage can also occur to the rechargeable battery when a fast charging current is applied to a battery which has been discharged beneath a minimum level. A trickle charging current, however, may be applied to such a deeply discharged battery.
Still further, when the voltage across the rechargeable battery is above a maximum value, a fast charging current should not be applied to the rechargeable battery. Again, a trickle charging current may be applied to the rechargeable battery without risk of damage to the battery.
The voltage levels taken across the battery and the ambient temperature of the battery may be measured prior to initiation of application of a fast charging current thereto. If the measured voltage levels are not beneath a maximum voltage level or above a minimum voltage level, application of the fast charging current to the battery should be prevented. Similarly, if the measured temperature levels are not beneath a certain maximum temperature level, and above a certain minimum temperature level, application of a fast charging current to the battery should similarly be prevented.
Such broad restrictions can, however, needlessly limit the times in which a fast charging current may be applied to a battery to recharge the battery. For instance, the ambient temperature level of a battery may be above a maximum level as a result of exposure of the battery for an extended period of time to direct sunlight. Relocation of the battery to a battery pocket of a battery charger may remove the battery from the exposure to the direct sunlight, but the ambient temperature level of the battery may not be reduced for a period of time. An indication of the ambient temperature level of the battery above the maximum temperature level may prevent the application of the fast charging current to the battery. However, relocation of the battery away from the direct sunlight, will result in a decrease in the ambient temperature level of the battery. Initial measurement of the temperature level of the battery prior to initiation of application of the fast charging current may prevent the application of the fast charging current. Conventionally, when the measured temperature and/or voltage levels of a battery positioned to be recharged is beyond an allowable range, application of a fast charging current is not initiated, and a trickle charging current is applied to the battery to recharge the battery thereby, even after the temperature and/or voltage level of the battery changes to be within the allowable range.
Additionally, if the voltage level across the battery is of a level close to the maximum or minimum allowable level, or if the ambient temperature level of the battery is of a value close to the maximum or minimum allowable level, application of the fast charging current to the battery may cause the minimum or maximum allowable levels to be exceeded. Conventionally, when the voltage and/or temperature level of a battery undergoing application of a fast charging current thereto exceeds maximum or minimum temperature and/or voltage levels, application of the fast charging current is immediately terminated.
In either situation, application of a fast charging current to the battery to recharge the battery thereby would not cause damage to the battery. Because initial measurement of the voltage level and/or temperature level of the battery is beyond allowable limits, application of a fast charging current to the battery is not initiated, or application of the fast charging current to the battery is terminated, after initiation, as a result of the temperature level and/or voltage level of the battery exceeding the allowable limits, even when such temperature level or voltage level changes are only transient.
What is needed, therefore, is a battery charging system which permits application of a fast charging current to a rechargable battery when the battery characteristics are within allowable limits to permit fast charging of the battery, and which continues application of the fast charging current even when the battery characteristics exceed the allowable limits by a predetermined amount during charging thereof.